Means for absorbing energy of impulse



0t 9, 1962 H. D. MaGDoNALD, JR., ETAL 3,057,263

MEANS FOR ABSORBING ENERGY OF IMPULSE Filed April 13, 1959 FIG.I.

1l s 'L ATTORNEYSZ 3,057,263 MEANS FOR ABSORBlNG ENERGY F IMPULSE Hugh D. MacDonald, lr., Philadelphia, and Robert W. Markgraf, Roslyn, Pa., and Norman J. Waecker, Masonville, NJ., assignors to the United States of America as represented by the Secretary of the Army Filed Apr. 13, 1959, Ser. No. 806,196 1 Claim. (Cl. 89-1) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention `described herein may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to energy absorbing means and more especially to devices which include means for absorbing energy such as that incident to the deceleration of a moving body.

A typical use of the invention is in the operation of a radio beacon ejection catapult. The beacon ejection catapult-s heretofore available have include a number of telescopic tubes which were separated at some point during the operation of the catapult. This type of operation is herein designated as open operation. It is not altogether satisfactory for the reason that (1) it involves a loud noise and the ejection of hot gas or flames at the point where the tubes are separated, (2) it results in the loss of a part of ythe tubes, and (3) it requires a relatively strong structure to withstand the instantaneous stoppage of the telescopic tubes as they are extended prior to their separation.

`The presence of hot 'gases and flames upon an aircraft obviously is objectionable for the reason that they may injure personnel or ignite combustible vapors or mixtures. In accordance with this invention, this difculty is avoided by the provision of an energy absorbing structure which functions without the ejection of gas from the telescopic tubes. This type of oper-ation is hereinafter designated as closed operation. It has the important advantages that (l) it makes the catapult safer, (2) it permits repeated use of the catapult, and (3) it permits the use of lighter parts for the reason that the energy of impulse is absorbed over a finite period of time and not instantaneously as in the case of the catapults heretofore available.

The invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope is indicated by the appended claim.

Referring to the drawings:

FIG. 1 is a sectional view of the device, and

FIG. 2 is a partial sectional view illustrating certain details thereof.

FIG. 1 of the drawing is a sectional View of a radio beacon catapult which includes a casing or outer tube liti, a telescoping tube 11, .an inner telescoping tube 12 and an inner tube 13.

The casing is fixed at one end to a base 14 by a thread 15 and a locking ring 16 and has its other end curved inwardly into engagement with a shearable diaphragm 17. The diaphragm 17 has a central opening 1'8 and functions to lock the tubes together in the standby condition of the catapult.

The inner tube 13 is open at one end, has a large diameter area at this end, and is closed at the other end by a tiring head 19 and a cartridge 20 which is surrounded by a seal ring 21. Extending from the tiring head 19 toward the opening 18 is a connection 22 which encloses any type of mechanism suitable for tiring the cartridge 20.

The telescopic tube 12 has at its inner end a large diameter area and at its outer end a small diameter area which slides along the large diameter area of the tube 13 upon relative movement between these two tubes. The telescopic tube 11 has `at its inner end a large diameter area and at its outer end a small diameter area which slides along the large diameter area of the tube 12 upon relative movement between these two tubes. Surrounding the tube `11 are (l) a support ring 23 which functions to maintain the tubes in their illustrated position in the standby condition of the catapult and (2) a frictional stop ring 24 which is smaller than and is slid along the large diameter area of the tube 11 by contact with the inwardly turned end of the tube 10 upon relative movement between the tubes 10 and `11.

A seal ring 25 is between the inner ends of the tubes 12 and 13 and a seal ring 26 is between the inner ends of the tubes 1d and 12. Each of the tubes 11, 12 and 13 has a wall thickness which is substantially uniform one end of the tube to the other.

The body to be ejected is ixed to a cap 27 which fits over the end of Athe tube 10 and leaves the aircraft with the ejected body.

In the operation of the device, the gas pressure generated by the firing of the cartridge 20 moves the tubes 11, '.12 and 13 together until the friction stop ring 24 engages the inwardly turned edge of the tube 10 and the tube 1\1 is brought to rest by friction -between the ting and the large diameter section of the tube |11. Thereafter the tubes 12 and :13 continue to move together until movement of the tube i12 is stopped by engagement of its large diameter section with the small diameter section of the tube 11. The tube 13 continues to move until its large diameter section frictionally engages the small diameter section o-f the tube 12. In order to provide a maximum of friction between the mating surfaces of the tubes, these surfaces may be lightly knurled, nely threaded, coated with emery dust or the like.

This mode of operation follows from the fact that the same gas pressure per unit area is applied to the bottom ends of the tubes .11, 12 and `13, which are very light and the cap 27 rests against the upper ends of these tubes with a weight of about fty pounds. Since the acceleration of the tubes equals pressure times the area divided by the mass, it follows that any tube tending to lag behind the 50 pound mass, or the mere weight of the cap 27, is quickly accelerated into engagement with the cap.

As indicated by FIG. 2, the tubes 111 and |12 have an extern-al roughened surface 29 at their enlarged ends and an internal roughened surface 28 at their contracted ends. The interior surface of the stop ring 24 and the exterior surface of the enlarged end of the tube 13 are similarly roughened.

The relation between the mating surfaces of the tubes is so calculated as to provide an interference fit such that no stress of the material exceeds its yield stress. While the yield stresses are not exceeded and the frictional engagement between the tubes is elastic, the energy absorbing process is inelastic and irreversible. This method of stopping the tube has the important advantage that it permits a finite s-topping time thus making possible the use of lighter and less expensive parts than are required where the motion of the tubes is stopped by butt or wedge joints and the like.

The herein disclosed simplicity of design permits ease of manufacture and assembly at low cost. The parts are interchangeable from one device to another. Maintenance is eliminated except for periodic replacement of the cartridge. And the tubes may be fabricated simply by expanding one end of a tube to a calculated diameter along a calculated length and contracting its other end to a calculated diameter along a calculated length.

We claim:

In a mass moving device, the .combination of a iirst tube having at one end an enlarged diameter exterior area and at the other end a reduced diameter interior area,

second tube having at one end means for retaining and firing an explosive cartridge and at the other end an enlarged diameter exterior area of a diameter greater than the diameter of said reduced diameter area of said first tube, said reduced diameter interior area of said rst tube and said enlarged diameter exterior area of said second tube forming annular friction means whereby relative movement between said first and second tubes is decelerated and separation of said first and second tubes is prevented,

third tube having at one end an enlarged diameter exterior area and at the other end a reduced diamcelerated and separation of said first a-nd third tubes is prevented,

a casing having an internal flange,

stop surrounding said third tube and having an interior diameter less than the diameter of said e11- larged diameter exterior area of said third tube, said enlarged diameter area of said third tube and said stop ring forming annular lfriction means whereby movement of said third tube is decelerated and stopped upon engagement of said stop ring with said flange, and

cap resting against the ends of said tubes and movable thereby.

References Cited in the le of this patent UNITED STATES PATENTS eter interior area of a diameter less than said enlarged diameter area of said first tube, said reduced rlow l? ii" diameter interior area of said third tube and said 2736236 ll Feb' 28 i 56 enlarged diameter exterior area of said first tube 20 2758807 Rslanm Agg' 14 1356 forming annular frlctron means whereby relative 912,902 Nessler NOV. 17', 1959 movement between said iirst and third tubes is de- 

